A simplified model of the back surface of the CCD is discussed. The model incorporates parameters which account for the important features of the back surface: a surface recombination velocity, an electric field which can assist in or oppose the collection of signal charge, and a field free region. Calculations using the model equations are presented to illustrate the effect of these parameters on the distribution of excess carriers and on the resulting quantum efficiency. The results indicate that only moderate fields are required to achieve high quantum efficiencies even at short wavelengths.